DECEMBER 20, 1906 | 
IN ATMOS IE 
search about the temple and its large monastery of 
nearly 4ooo priests. He devotes several pages to the 
sacred tree, which has been identified for him as 
Syringa Giraldiana, K. Schneider. A word of praise 
is due for the excellent illustrations, many of them 
from photographs by Frau Filchner, who accompanied 
her husband in his travels. Altogether the book forms 
a complete guide to the place, and is admirably 
produced at such a marvellously cheap price as is only 
possible on the Continent. L. A. WADDELL. 
A Century's Progress in Astronomy. By Hector 
Macpherson, jun. Pp. xi+246. (London: W. 
Blackwood and Sons, 1906.) Price 6s. net. 
IN attempting to crowd an account of a century’s 
progress in one of the most progressive of sciences 
(during the last century) into 238 pages of well-dis- 
played print we fear that Mr. Macpherson has 
attempted too much in too little space. The volume 
will certainly be found useful for reference as an 
astronomical ‘‘ Who’s Who,” but we fear that the 
general reader will have but a hazy idea of the true 
meaning of the century’s progress after perusing it. 
The first two chapters, occupying more than one- 
sixth of the total reading matter, deal with Herschel, 
the ‘‘ pioneer ’’ and ‘‘discoverer,’’ and are full of 
interest and information. The subsequent chapters 
(iii. to ix.) treat of the celestial bodies in the con- 
ventional order, and as completely as can be expected 
in so confined a space, the more important discoveries, 
e.g. those by Schwabe, Janssen, Lockyer, Tacchini, 
and others concerning the sun, receiving a_ fair 
amount of attention. 
The concluding chapters (x. to xiv.) deal with the 
spectroscopic and variable-star work, stellar systems, 
stellar distribution, and celestial evolution, the various 
theories and researches in each branch being passed 
in rapid review. 
Speaking generally, Mr. Macpherson’s information 
is up-to-date, and includes most of the events in the 
century’s work, but in some few cases this is not so. 
For example, we are surprised to find that although 
the names of some dozen foreign double-star observers 
are given (p. 201), no English name has been found 
worthy of inclusion, not even that of Thomas Lewis. 
Again, we believe that Sir Norman Lockyer’s later 
researches have, by a natural order of progress, 
advanced his temperature classification beyond the 
stage where the Sirian stars were thought to illustrate 
the acme of temperature. A bibliography giving 
references to the original works so briefly epitomised 
in this volume would be of great value, but the book 
contains no references. AWE Bis AR 
The World’s Calendar. 
Wiles. 
net. 
Invented by the Rev. J. P. 
(London: G. Philip and Son.) Price 2s. 
Mr. Wites has devised a very ingenious toy which 
will exhibit the day of the week corresponding to 
any calendar date and also Easter-day for any year. 
We do not think that any better mechanical method 
could have been constructed, but we are not much in 
sympathy with contriving any device of the kind. 
The information given is not often required by most 
of us, and those who do require it had far better 
work from a concise tabular statement. 
As a Christmas present it would probably give satis- 
faction. Perhaps Mr. Wiles contemplated this in 
bringing his calendar out in November. From this 
point of view it deserves success, and will prompt 
the curiosity of some to try thoroughly to understand 
the construction. 
NO. 1938, VOL. 75 | 
LELTDLT ERS) DOME EDITOR. 
[The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of Nature. 
No notice is taken of anonymous communications. ]| 
Cutting a Round Cake on Scientific Principles. 
CHRISTMAS suggests cakes, and these the wish on my part 
| to describe a method of cutting them that I have recently 
devised to my own amusement and satisfaction. The 
problem to be solved was, “‘ given a round tea-cake of some 
5 inches across, and two persons of moderate appetite to 
eat it, in what way should it be cut so as to leave a 
minimum of exposed surface to become dry?”’ ‘The 
ordinary method of cutting out a wedge is very faulty in 
this respect. The results to be aimed at are so to cut 
the cake that the remaining portions shall fit together. 
Consequently the chords (or the arcs) of the circumferences 
Ok 
Broken straight lines show intended cuts. Ordinary straight lines show 
the cuts that have been made. The segments are kept in apposition 
by a common elastic band that encloses the. whole. In the above 
figures about one-third of the area of the original disc is removed by 
each of the two successive operations. 
of these portions must be equal. The direction of the first 
two vertical planes of section is unimportant; they may 
be parallel, as in the first figure, or they may enclose a 
wedge. The cuts shown on the figures represent those 
made with the intention of letting the cake last for three 
days, each successive operation having removed about one- 
third of the area of the original disc. A common india- 
rubber band embraces the whole and keeps its segments 
together. I. 
Anode Rays. 
In the Deutsch. Phys. Gesell. (Verh. 8, 21, pp. 559-566, 
November 15) there appears a paper by Gehrcke and 
Reichenheim under the title of ‘‘ Anode Rays.” 
By means of a special construction a discharge is sent 
through a tube in which the anode consists of an inorganic 
salt placed on platinum foil and heated to a dull red heat 
by an auxiliary current. The salts used are mostly 
chlorides. In these circumstances a brilliant bundle of 
coloured rays is emitted by the anode, but this emission 
soon ceases. These rays the authors call ‘‘ anode rays.’” 
Their positive charge is demonstrated by shooting them 
into a Faraday cylinder and by their magnetic deflection. 
These results appear to me to be attributable to the 
emission of positive ions by heated salts, which has already 
been investigated by Mr. Garrett and myself (Phil. Mag., 
October, 1904). Mr. Garrett has continued the work de- 
scribed there, and finds that most halogen salts behave in 
a similar manner, and that this positive emission can 
readily be detected at ordinary temperatures. Both the 
number and velocity of the ions increase rapidly as the 
temperature is raised or pressure lowered, and in the paper 
mentioned we found that the emission ceased when the 
heating was continued. Allowing for the difference in 
temperature, Gehrcke and Reichenheim’s results and ours 
appear to be different aspects of the same phenomenon. 
We are now seeking to determine what exactly the positive 
ions are, and in this connection the observation is of 
interest that the anode rays. give very sharp lines of the 
metal involved, when coupled with J. Stark’s discovery 
that the canal rays are the emitters of the hydrogen-line 
spectrum. R. S. WiLtows. 
Cass Institute, E.C., December 17. 
